The present invention is related to disc drive data storage systems and, more particularly, to a method of controlling curvature of a transducing head, such as a hydrodynamic bearing slider.
Disc drives of the xe2x80x9cWinchesterxe2x80x9d type are well known in the industry. Such drives use rigid discs coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor, which causes the discs to spin and the surfaces of the discs to pass under respective head gimbal assemblies (HGAs). Head gimbal assemblies carry transducers which write information to and read information from the disc surface. An actuator mechanism moves the head gimbal assemblies from track to track across the surfaces of the discs under control of electronic circuitry. The actuator mechanism includes a track accessing arm and a load beam for each head gimbal assembly. The load beam provides a preload force which urges the head gimbal assembly toward the disc surface.
The head gimbal assembly includes a gimbal and a slider. The gimbal is positioned between the slider and the load beam to provide a resilient connection that allows the slider to pitch and roll while following the topography of the disc. The slider includes a slider body having a bearing surface, such as an air bearing surface, which faces the disc surface. As the disc rotates, the air pressure between the disc and the air bearing surface increases, which creates a hydrodynamic lifting force that causes the slider to lift and fly above the disc surface. The preload force supplied by the load beam counteracts the hydrodynamic lifting force. The preload force and the hydrodynamic lifting force reach an equilibrium which determines the flying height of the slider. The transducer is typically mounted at or near the trailing edge of the slider.
In some applications, the slider flies in close proximity to the surface of the disc. This type of slider is known as a xe2x80x9cpseudo-contactxe2x80x9d slider, since the bearing surface of the slider can occasionally contact the surface roughness of the disc. In other applications, the slider is designed to remain in direct contact with the disc surface with substantially no air bearing. These sliders are referred to as xe2x80x9ccontact recordingxe2x80x9d sliders.
It is often desirable to fabricate a slider such that the bearing surface has a positive curvature along the length and width of the slider. Length curvature is known as crown curvature. Width curvature is known as cross or camber curvature. The proper setting and control of crown and cross curvature improves flying height variability over varying conditions, improves wear on the slider and the disc surface, and improves takeoff performance by reducing stiction between the slider and the disc surface. In a typical slider fabrication process, crown or cross curvature is created by lapping the bearing surface on a spherically-shaped lapping surface or on a flat lapping surface while rocking the slider body back and forth in the direction of the desired curvature. The amount of curvature is determined by the radius of the rocking rotation. This lapping process is difficult to control and results in large manufacturing tolerances. More efficient and controllable methods of effecting air bearing surface curvature are desired.
U.S. Pat. No. 5,442,850 discloses a method of controlling curvature by inducing a preselected amount of compressive stress within a selected section of the bearing surface by impinging the section with particles for a preselected amount of time. U.S. Pat. No. 5,266,769 discloses a process of controlling slider curvature in which the air bearing surfaces are first patterned and then a chosen pattern of stress is produced on the back side of the slider by laser oblation or sand blasting to selectively remove stressed material and thereby create a desired crown and cross curvature of the bearing surface.
U.S. Pat. No. 4,910,621 discloses a method of producing curvature in a slider by creating a groove in the leading edge of the slider, placing a sealing material in the groove and then melting and stiffening the sealing material in the groove. The sealing material has an adhesive property upon melting and a shrinking property upon stiffening which causes lengthwise curvature at the leading edge of the slider. U.S. Pat. No. 5,220,471 discloses a slider having a longitudinal linear groove formed in a surface which is opposite the disc-opposing surface. The groove creates tensile stresses which cause the disc-opposing surface of the slider to be a curved surface in a convex form.
U.S. Pat. No. 5,982,583 discloses a method of effecting slider curvature through the application of laser-induced anisotropic tensile stress, which allows one of the crown and cross curvature to be changed to a greater extent than the other curvature. In addition, Seagate Technology, Inc. has used a process of creating scratches on the back side of the slider (the side opposite to the air bearing), lapping the bearing surface flat and then laser heat treating the scratches to reduce compressive stress caused by the scratches and thereby cause a positive curvature change in the bearing surface. This process is discussed in U.S. application Ser. No. 08/662,849, Filed Jun. 12, 1996.
While the above methods improve curvature control, these methods are still not entirely effective in accurately and independently achieving desired curvature values for both crown and cross curvature on the same slider.
One aspect of the present invention is directed to a method of controlling cross and crown curvatures of a bearing surface of a disc head slider. In the method, a measure of the cross and crown curvatures is obtained. Material stresses are altered in a working surface of the slider within a cross curvature adjust area based on the measure of the cross curvature. The cross curvature adjust area is defined such that altering material stresses within the cross curvature adjust area induces a change in the cross curvature while inducing substantially no change in the crown curvature. Material stresses are altered in the working surface of the slider within a crown curvature adjust area based on the measure of the crown curvature. The crown curvature adjust area is defined such that altering material stresses within the crown curvature adjust area induces a change in the crown curvature while inducing substantially no change in the cross curvature.
Another aspect of the present invention is directed to a method of adjusting cross and crown curvatures on a bearing surface of a disc head slider, which has a back surface that is opposite to the bearing surface, leading and trailing edges, first and second side edges, a longitudinal axis and a transverse axis. A first number of laser scan lines are selectively formed on the back surface, parallel to the transverse axis and within each of first and second rectangular cross curvature adjust bands, as a function of a measure of the cross curvature. The first and second rectangular cross curvature adjust bands are defined along the leading and trailing edges, respectively, of the working surface and peripheral to a central area of the working surface. A second number of laser scan lines are selectively formed on the back surface, parallel to the longitudinal axis and within each of first and second rectangular crown curvature adjust bands, as a function of a measure of the crown curvature. The first and second rectangular crown curvature adjust bands are defined along the first and second side edges, respectively, of the working-surface and peripheral to the central area of the working surface.
Yet another aspect of the present invention is directed to an apparatus for controlling cross and crown curvatures of a bearing surface of a disc head slider. The apparatus includes a light source adapted to produce a light beam capable of altering material stresses in a working surface of the slider. A device is coupled to the light source for scanning the light beam across the working surface in a pattern. The pattern is selected to alter material stresses in the working surface within a cross curvature adjust area so as to induce a change in the cross curvature while inducing substantially no change in the crown curvature and within a crown curvature adjust area on the working surface so as to induce a change in the crown curvature while inducing substantially no change in the cross curvature.